1. Field of the Invention
This invention relates to an air suspension, and more particularly to a strut type air suspension used for an automobile, which has a variable spring constant.
2. Description of the Prior Art
A strut type air suspension having a variable spring constant comprises a shock absorber and an air spring. The air spring is constituted from a main air chamber formed by mounting a housing on a piston rod of the shock absorber while spanning a diaphragm between the housing and a cylinder of the shock absorber and an auxiliary air chamber formed of a tank, both chambers being filled with compressed air. The air spring can obtain hard spring characteristics when the main air chamber is shut off from the auxiliary air chamber and soft spring characteristics when the main air chamber communicates to the auxiliary air chamber. Thus, the spring characteristics can be changed according to the travelling condition of an automobile to ensure a good ride and controllability.
However, since the tank and a valve unit incorporated in piping interconnecting the tank and the housing to afford and shut off communication between the auxiliary and main air chambers were conventionally provided independently spaced from the housing, spaces were needed for installing respectively the valve unit and the tank so that not only the effective space of a compartment was narrowed, but also the adjustment of spring constant was difficult as the resistance of the piping was increased depending upon the length thereof. Also, since the valve unit was mounted exposed to the outside, the operational noise in operation of the valve unit was transmitted to the compartment to give an unpleasant feeling to passengers.